1. Field of the Invention
The present invention relates to a V-belt-type automatic transmission for a vehicle, and more particularly to a V-belt-type automatic transmission including centrifugal weights mounted on a vehicle such as a motorcycle.
2. Background Art
In the related art, a V-belt-type automatic transmission mounted on a motorcycle includes a V-belt wound around and extending between a drive pulley provided at the end of a crankshaft of an internal combustion engine and a driven pulley provided on a driven shaft linked to a rear axle by a final reduction gear.
When the rotational speed of the internal combustion engine increases with respect to the drive pulley, a movable pulley pressed by a weight roller moving radially outward under centrifugal force approaches a fixed pulley piece. Concurrently, a movable pulley piece urged by a spring moves away from the fixed pulley piece with respect to the driven pulley and against the spring force. Therefore, a wrapping radius of the V-belt of the drive pulley and driven pulley is automatically changed, and the gear ratio decreases.
A V-belt-type automatic transmission is shown, for example, in Japanese Patent Laid-open Publication No. Sho. 59-113353. A middle gear ratio is obtained having a value between two gear ratios. The middle gear ratio is set in a middle speed range between a low-speed rotation range where the gear ratio is set at maximum gear ratio, and a high-speed rotation range where the gear ratio is set at minimum gear ratio.
In a fourth embodiment of the transmission apparatus disclosed in the Japanese Patent Laid-open Publication, a pair of sloped surfaces on which a weight rolls are provided on a rear surface of a right pulley element of a drive pulley. The stopper surface of one of the pair of sloped surfaces is arranged more radially inward than the stopper surface of other sloped surface, and the weight comes into contact with the stopper surface of the other sloped surface in the middle-speed rotation range. Therefore, radial movement is prevented and the middle gear ratio is set.
Generally, in a driven pulley of a V-belt-type automatic transmission, a movable pulley piece is urged towards a fixed pulley piece by the spring force of a cylindrically-shaped an compressed coil spring. The moveable pulley piece moves in an axial direction against or urged by the spring force in the event of change in the wrapping radius of the V-belt. A spring guide is also provided inside the spring for preventing the spring from collapsing or bending.
The right pulley element of the transmission disclosed in the Japanese Patent Laid-open Publication moves further in the axial direction by the weight rolling on the other sloped surface in the high-speed rotation range. A gap in the axial direction is arranged between the weight coming into contact with the stopper surface of the other sloped surface and the right pulley element. The gap prevents weight from moving in the radial direction.
As a result, due to engine vibrations, etc., there is relative movement in the axial direction between the right pulley element and the weight. There is additional movement between a cover sandwiching the right pulley element and the weight. The weigh can collide with adjacent parts causing abrasion. In addition, the weight is prevented from moving smoothly in the radial direction, therefore possibly causing difficulty in smooth transmission.
As a result of friction with a spring guide partly coming into contact with the internal circumference of the spring when the spring is expanded or contacted, or as a result lack of smooth spring contraction due to contact of the spring against a tip of the spring guide during spring contraction, the movable pulley piece may be prevented from moving smoothly with respect to the driven pulley and transmission may not be executed smoothly.
The present invention overcomes the shortcomings associated with the related art and achieves other advantages not realized by the related art. An object of the present invention is to provide a V-belt-type automatic transmission for vehicles that is capable of smooth transmission between gear ratios and operating speeds.
These and other objects are accomplished by A V-belt automatic transmission for a vehicle comprising a drive pulley provided on a driveshaft, the drive pulley further including a drive side moveable pulley piece, a drive side fixed pulley piece, a cam plate, a plurality of centrifugal weights arranged between the drive side movable pulley piece and the cam plate, the drive side movable pulley piece moveable in an axial direction of the driveshaft and rotateable with the cam plate on the driveshaft, and a plurality of pulley side guide surfaces for guiding the plurality of centrifugal weights formed extending in a radial direction of the driveshaft on a rear surface of the drive side movable pulley, the plurality of centrifugal weights including a first set of centrifugal weights and a second set of centrifugal weights, each centrifugal weight of the first set is lighter than each centrifugal weight of the second set; a driven pully provided on a driven shaft; a V-belt having a wrapping radius and wrapped around the drive pulley and the driven pulley for transmitting torque from the drive shaft to the driven shaft, wherein the wrapping radius is changed based on a movement in a radial direction along each pulley side guide surface of the plurality of centrifugal weights arranged between a pulley side guide surface provided on the drive side movable pulley piece and a cam side guide surface provided on the cam plate; and a maximum gear ratio in a low-speed rotation range and a minimum gear ratio in a high-speed rotation range set when the plurality of centrifugal weights are prevented from moving in a radial direction at a speed faster than a prescribed rotational speed in at least one middle-speed rotation range to thereby set and define a middle gear ratio in each middle-speed rotation range.
These and other objects are further accomplished by a V-belt automatic transmission for a vehicle comprising a drive pulley provided on a driveshaft, the drive pulley further including a drive side moveable pulley piece, a drive side fixed pulley piece, a cam plate, a plurality of centrifugal weights arranged between the drive side movable pulley piece and the cam plate, the drive side movable pulley piece moveable in an axial direction of the driveshaft and rotateable with the cam plate on the driveshaft, and a plurality of pulley side guide surfaces for guiding the plurality of centrifugal weights formed extending in a radial direction of the driveshaft on a rear surface of the drive side movable pulley, the plurality of centrifugal weights including a first set of centrifugal weights and a second set of centrifugal weights, each centrifugal weight of the first set is lighter than each centrifugal weight of the second set; a driven pully provided on a driven shaft; a V-belt having a wrapping radius and wrapped around the drive pulley and the driven pulley for transmitting torque from the drive shaft to the driven shaft, wherein the wrapping radius is changed based on a combination of a first movement in a radial direction along each pulley side guide surface of the plurality of centrifugal weights arranged between a pulley side guide surface provided on the drive side movable pulley piece and a cam side guide surface provided on the cam plate and second movement of the drive side movable pulley piece against a spring force created in response to the movable pulley piece being moved by centrifugal force of the centrifugal weights; and a maximum gear ratio in a low-speed rotation range and a minimum gear ratio in a high-speed rotation range set when the plurality of centrifugal weights are prevented from moving in a radial direction at a speed faster than a prescribed rotational speed in at least one middle-speed rotation range to thereby set and define a middle gear ratio in each middle-speed rotation range.
According to the present invention, excessive vibration and collisions between moving parts is reduced. In addition, noise occurring from normally occurring vibrations is transmitted throughout the transmission of the present invention in a manner that further suppresses noise. Since vibration is reduced, premature wear of adjacent parts in contact with another is further reduced, thereby extending operating life of all transmission components. Finally, smooth, regular transmission through a series of gear ratios and engine rotational speeds is achieved with all of the benefits of noise reduction and wear reduction.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.